Dehydration is the medical condition in which a horse’s body has lost more fluid than it has taken in, creating a net deficit of water and electrolytes. The condition exists on a continuum: mild dehydration (three to five percent bodyweight loss in fluid) causes reduced performance and dry mucous membranes, while severe dehydration (above eight percent) carries risk of circulatory collapse, kidney failure, and death if untreated.
The skin pinch test is a primary field indicator: tenting of the skin for more than two seconds after release indicates significant dehydration. Gum assessment provides a second data point — normal gums are pink and moist with a capillary refill time under two seconds; dehydrated horses show tacky, pale, or gray gums and prolonged refill. In severe cases, sunken eyes, an elevated heart rate, and signs of impaction and colic risk accompany fluid deficit. Treatment requires oral or intravenous fluid replacement, with electrolyte supplementation when losses are primarily from sweating.
Prevention centers on consistent water access. An adult horse requires twenty to forty liters of water per day at rest, with requirements rising sharply during exercise and hot weather. Winter dehydration is underrecognized; horses often refuse cold water and reduce intake, increasing impaction colic risk. Feed management plays a role: high forage diets increase water consumption naturally. See also clinical causes and treatment for a full clinical guide covering causes, assessment protocol, and recovery.
Further Reading
Background on the physiology of dehydration is available in the Wikipedia article on dehydration. Clinical management of fluid deficits in horses is addressed in the Metabolic Disorders of Horses chapter of the Merck Veterinary Manual.